What is the lifetime of a photon in a medium?

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Discussion Overview

The discussion centers around the concept of the lifetime of a photon when it travels through a medium, specifically water. Participants explore the implications of light's reduced speed in a medium and whether this affects the notion of a photon's lifetime.

Discussion Character

  • Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions how the slowing of light in a medium affects the lifetime of a photon.
  • Another participant asserts that the lifetime of a photon is not affected by its speed in a medium.
  • A different viewpoint emphasizes that light should be analyzed as an electromagnetic wave in this context, suggesting that the concept of photons is not applicable unless quantum mechanical effects are significant.
  • One participant reiterates that light appears to slow down in a medium due to the superposition of incoming light and re-radiated light by atoms, referencing a specific chapter from "The Feynman Lectures on Physics" for further reading.

Areas of Agreement / Disagreement

Participants express differing views on whether the concept of a photon's lifetime is relevant when discussing light in a medium. There is no consensus on the implications of light's speed reduction on photon lifetime.

Contextual Notes

There are unresolved assumptions regarding the applicability of photon concepts in classical versus quantum contexts, and the discussion does not clarify the conditions under which these concepts may or may not hold.

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When light travels through a medium like water, it slows down and its speed is no longer equal to c. How does this affect the life time of the photon?
 
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It doesn't.
 
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Light traveling through a medium like water cannot be usefully thought of as photons moving through the water. The light is an electromagnetic wave, and we analyze this problem as a wave moving through the medium.

Photons only come into the picture when quantum mechanical effects are significant, and they aren't in this problem.
 
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docnet said:
When light travels through a medium like water, it slows down and its speed is no longer equal to c.

When light travels through a medium like water, it appears to slow down. The apparent "slower speed" is the result of the superposition of two radiative electric fields: the incoming light, traveling at speed ##c##, and the light re-radiated by the atoms in the medium in the forward direction, traveling at speed ##c##, too. In case one wants to understand the essential aspects of the phenomena, I recommend to read chapter 31 “The Origin of the Refractive Index” in “The Feynman Lectures on Physics, Volume I". (http://www.feynmanlectures.caltech.edu/I_31.html).
 
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